Apparatus for overcoming the residual magnetism in an electromagnetic door holder



Oct. 13, 1970 B. J. CRANE ETAL 3,533,652

APPARATUS FOR OVEROOMING THE RESIDUAL MAGNETISM IN AN ELECTROMAGNETIC DOOR HOLDER Filed Aug. 14. 1967 .54 73 j u I /r fig? United States Patent 3,533,652 APPARATUS FOR OVERCOMING THE RESIDUAL MAGNETISM IN AN ELECTROMAGNETIC DOOR HOLDER Burke J. Crane, Lombard, and Frank S. Pasek, Westchester, Ill., assignors to Rixson Inc., Franklin Park, 111., a corporation of Illinois Filed Aug. 14, 1967, Ser. No. 660,269 Int. Cl. Ec 17/56; H01f 7/20 US. Cl. 292251.5 3 Claims ABSTRACT OF THE DISCLOSURE Electromagnetic door holder in which an armature is attached to a door and an electromagnet. is attached to a fixed structure, or vice versa, so that the door may be held adjacent the fixed structure when the electromagnet is energized and the armature engages it, together with structure which assures release of the door from its held position, in spite of residual magnetism, when the electromagnet is deenergized.

DESCRIPTION OF THE INVENTION In swinging doors of the automatic closure type having a spring closure mechanism for automatically swinging the door to closed position, it is a frequent practice to provide an electromagnetic hold-open device which will hold the door in Open position magnetically as long as the electromagnetic device remains electrically energized. When electrically energized, it is normally operative to overcome the door closing torque exerted by the spring door closer, so as to hold the door in open position. When the circuit to the holding electromagnet is interrupted, it is intended that the door holding device release the door for immediate closure by the automatic spring door closing device. However, this electromagnetic release does not always occur, because of the holding action of residual magnetism tending to remain in the magnetically attracting parts of the apparatus.

The principal object of the present invention is to provide a door release in the form of a reaction structure, associated with the electromagnetic device, which will always overcome the effect of this residual magnetism, whenever the flow of current to the door holding electromagnet is interrupted so that the door may be swung to a closed position.

The magnetically attracting parts comprise a stationary solenoid winding and core which are fixedly mounted preferably on the door frame, wall or the like, and a cooperating movable magnetically attracted armature preferably mounted on the swinging door in position to be attracted by the solenoid when the door is opened and the solenoid is energized.

Another object of the invention is to provide the reaction structure in the core or in the armature of the door holder device. For example, this reaction structure comprises a releasing button or plunger extending axially of the core, and a helical compression spring normally tending to hold the plunger extended from the core into a position where it will be engaged and moved by the armature to cause compression of the spring when the armature is attracted to the electromagnet. Alternately, the spring loaded plunger can be supported in the armature structure.

Another object of the invention is to provide improved adjusting apparatus for adjusting the degree of energy storage of the spring.

Another object of the invention is to so construct the above assembly of the electromagnet, the releasing plunger,

and the helical compression spring, that if desired, this stationary assembly can be fastened to a conventional electrical outlet box mounted adjacent to the door frame in the wall.

The electromagnetic solenoid winding and core are mounted in a cup-shaped magnetic shell or housing which has its open edge functioning as one pole of the mag netic circuit. The other magnetic pole consists of the end face of the core. With our invention both the core and cup can be made of ordinary grades of carbon steel which are less expensive and easier to form and machine. These characteristics, however, result in greater residual magnetism but the present invention is adapted to overcome that disadvantage.

Heretofore, the end face of the core has been located at a level lower than the pole defined by the outer rim of the shell. For example, in one commercial product the difference in level was .006 inch and only a tolerance of plus or minus .001 inch was heretofore permissible in order to asure proper magnetic attraction, as well as release. Now, however, with the present invention, the difference in level of the two planes can be .004i-.002 inch, or 0031.003 inch. With the tolerances being less severe, the cost of producing and assembling the parts is reduced.

Other objects and advantages of the invention will be apparent from the following detailed description of certain preferred embodiments thereof.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS FIG. 1 is a plan view of a conventional swinging door installaton employing a pneumatic or hydraulic door check with spring means for causing closing of the door, showing the present improved electromagnetic door holder and door release operating in conjunction therewith for holding the door open when desired;

FIG. 2 is an enlarged vertical sectional view taken approximately on the plane of line 2-2 of FIG. 1, with some portions shown in elevation, and with the electromagnetic structure and armature structure shown slightly separated prior to engagement;

FIG. 3 is a similar type of sectional view on a larger scale of a modified construction, taken approximately on the same plane;

FIG. 4- is a similar type of sectional view of another modified embodiment; and

FIG. 5 is a perspective view on reduced scale of the armature structure and its supporting frame adapted to be carried by the door.

Referring to FIGS. 1 and 2, a conventional spring closed swinging door is indicated at D, hinged at 12 for swinging movement from the open position illustrated in solid lines to the closed position C in the doorway 18. A spring actuated door closer 20 which is usually pneumatically or hydraulically checked, normally tends to swing the door from the open position back to the closed position C by reason of a spring operator in the door closer.

The present improved electromagnetic door holder and release device, designated 25 in its entirety, is shown in FIGURE 1 as performing its intended function of holding the door in its open position against the spring closing action of the automatic spring door closer 20. This improved door holder 25 comprises a stationary electromagnet structure 27 which is mounted in a supporting frame or housing 29 which is adapted to be fastened to a wall, frame, or like stationary supporting structure 30, substantially at the desired open position of the door. The supporting frame 29 is designed to be connected directly over, and to, an outlet box 31, if desired.

Cooperating with the electromagnetic structure 27 is an armature structure 32 mounted on the door D and adapted to be magnetically attracted into door holding contact with the stationary electromagnetic structure 27 when it is desired that the door be held in open position. At such time the electromagnetic unit 27 is electrically energized through a control circuit which is responsive either to manual or two automatic switching apparatus. The circuit and switching apparatus are of a known type and are not illustrated since they form no part of our invention.

Referring first in detail to the stationary electromagnetic structure 27, this comprises an outer fixedly mounted housing 29 preferably of a nonmagnetic metal. Formed centrally in the front wall 33 of such housing 29 is a relatively large circular opening 35 through which extends the circular electromagnetic structure 27. Also formed in this front wall 33 above and below the large central opening 35 are fastening holes 37 for receiving fastening screws which may thread into tapped holes in a bracket afiixed in the outlet box 31, for example. The electromagnetic coil 50 is mounted in a cylindrical cup-shaped magnetic housing 54 which has its rear wall or base 56 secured to a fiat mounting plate 58. This mounting plate 58 is secured by corner mounting screws 59 which pass through corner holes in the plate 58 and thread into tapped bosses -60 integral with the housing 29 and projecting rearwardly from the front wall 33 thereof. Disposed centrally of the coil 50 is a magnetic core 62 having a front face 64 directed toward the armature 32.

The projecting open end of the cup-shaped housing 54 has a surface 66 which extends slightly beyond the front face of the coil 50 and also slightly beyond the front face 64 of the central core '62.

As indicated above, the distance between the planes defined by the surfaces 64 and 66 can satisfactorily be .004i.002 inch or 8031.003 inch.

The armature structure 32 comprises a steel armature plate 71 secured by an epoxy adhesive, or by other suitable means to a non-magnetic plate 73 having a central flange 75 which has a pivotal mounting on an adjustable supporting structure 77 carried by the bifurcated end 79 of a mounting frame or housing 81. Frame 81 is secured to the side of the door D by a pair of bolts 83, 83 which pass through aligned holes in mounting plate 84 and door D and are threaded into tapped sockets 85, 85 of frame 81. The pivotal mounting is adapted to have the armature plate 71 moved to, and then secured in, a plane which makes it parallel to the end surfaces 64 and 66 of the core 62 and cup-shaped housing 54, respectively.

The structure for overcoming the residual magnetism tending to remain in the electromagnets cup-shaped magnetic housing 54, and the central magnetic core 62, is shown in FIG. 2 associated with the armature structure 32. It is a reaction structure which comprises a stepped, spring-loaded thrust button or plunger 91. -It and the coiled spring 93 are mounted in a stepped bore formed by a smaller diameter hole 95 in armature plate 71 and a larger diameter hole 97 formed in plate 73 and its flange 75. The inner end of the spring 93 abuts against the bottom of the hole 97 and the outer end abuts against the bottom of a socket or counterbore in the plunger 91. The projecting end of the plunger 91 is of reduced diameter so that a stop shoulder 99 is formed which abuts against the inner surface of the armature plate 71. The outer exposed end of the plunger 91 is adapted to bear against the end face 64 of the core 62 of the stationary electromagnetic unit 27. When the plate 71 of the armature structure 32 is magnetically held to the electromagnetic structure 27, plunger 91 is pressed inwardly of the stepped bore and spring 93 is compressed. When the coil 50 is deenergized, spring 93 acting through plunger 91 presses against the core '62 and assures separation of armature plate 71 from the electromagnetic structure 27.

This arrangement allows the use of grades of iron for the electromagnetic and armature structures, which grades are high in carbon content, easier to machine and less expensive, and allow a wider tolerance in positioning the plane of the surfaces 64 and 66 of core 62 and cup 54.

In the operation of this embodiment, when it is desired to pass through the doorway 18 by manual opening of the door, to be followed by the immediate automatic return of the door to closed position under the action of the spring pressed door closer 20, the circuit to the electromagnetic winding or coil 50 is not energized. Hence, there is no magnetic holding actionbetween the electromagnetic and armature structures and accordingly the structures do not function and the door returns immediately to closed position.

However, when it is desired that the door remain in open position, the electromagnetic winding 50 is energized through any suitable circuitry and switch and, when the armature plate 71 comes into juxtaposition to the cup 56 and the electromagnetic core 62 the armature structure 27 locks up magnetically and holds the door in this open position as long as there is a current flow through the winding, unless the door is manually forced in a closing direction to bring the armature plate 71 out beyond the magnetic influence of the electromagnetic structure 27. The electromagnetic energization may be continued either for a short duration, as for permitting objects to be moved quickly through the door, or for a few hours, or indefinitely by merely allowing the energizing current to continue for the appropriate length of time.

In FIG. 3 we have illustrated a modified construction in which the spring loaded plunger 91 has a compression spring 93' coacting therewith, and both are carried by the electromagnetic structure rather than by the armature structure. The spring normally tends to push the plunger 91' toward the armature plate 71 of the armature structure 32 on the door. There is a counterbore 97 for the compression spring 93' and for the enlarged portion of plunger 91', and there is a smaller diameter bore through a magnetic disk 100 which is secured to the end of core 62'. At the junction of bores 93' and 95 is a stop shoulder 99' against which strikes the outer face of the enlarged portion of the plunger 91'. Plunger 91 extends outwardly beyond the end surface 64' of disk 10 and beyond the plane of surface 66 of the cup 54' so that it can be engaged and pressed inwardly by armature plate 71' to compress spring 93'.

FIG. 4 shows a modification of FIG. 3. Extending outwardly from the counterbore 97 to the other end of the core 62" is a threaded bore 102 through which screws an adjusting machine screw 103. The innermost end of spring 93" is seated in said bore 102 and its other end bears against the flat end of the plunger 91". Rotation of the screw head 103 increases or decreases the compression of the spring 93". If limited spaced precludes the use of a headed machine screw, the screw may be formed as a set screw of proper diameter and length with a socket for a wrench in its end. In each of the embodiments of FIGS.

3 and 4 the armature structure 32 has the same mounting on the door D as previously described relative to FIGS. 1 and 2, and the reference numerals for the structures of FIGS. 3 and 4 are the same as the reference numerals for the corresponding structures of FIG. 2 but with the addition to said numerals of a prime designation and a double prime designation, respectively.

Other modifications and uses of our invention will be readily suggested by this disclosure to those skilled in the art, so this invention is not to be considered as limited to the herein described examples.

We claim:

1. An electromagnetic door holder having an electromagnetic structure with magnetizable means and having a cooperable armature structure, said magnetizable structure being adapted to be disposed at a selected position and the armature structure being adapted to be secured to a movable door whereby the door may be held at said selected position when the electromagnetic structure is energized and the armature structure engages the magnetizable means, a housing for the electromagnetic structure adapted to be securely fixed at said selected location for supporting the electromagnetic structure, a frame adapted to be rigidly secured to a door to support the armature structure at a position where it may directly engage the electromagnetic structure at the selected posi tion when the door is opened, said armature comprising a magnetizable plate having a passage therethrough and being secured to a non-magnetic member which has a bore of larger diameter than said passage, reaction means having a spring pressed plunger which is mounted for reciprocal movement in said armature structure and protrudes therefrom, said spring being disposed in said bore and said bore being coaxially aligned with said passage, said spring pressed plunger having a stepped configuration with a reduced end guided in said passage and adapted to extend outwardly thereof to engage and be compressed by the electromagnetic structure, and said plunger having a larger end fitting in and guided by said bore and engageable by the spring, the plunger being adapted to engage said electromagnetic structure whereby it is depressed and stores energy in the spring, and said plunger being adapted to push against said electromagnetic structure and to react against said armature structure is deenergized, to separate said structures.

2. The improvement of claim 1 wherein said frame for the armature structure has a bifurcated portion, and wherein said non-magnetic member has a flange extending away from said bore and pivotally mounted on an adjustable supporting structure within said bifurcated portion.

3. An electromagnetic door holder having an electromagnetic structure with magnetizable means and having a cooperable armature structure, with one of said structures being adapted to be disposed at a selected position and the other being secured to a movable door, whereby the door may be held adjacent said selected position when the electromagnetic structure is energized and the armature structure engages the magnetizable means, said electromagnetic structure having a core with a stepped passage at its outer end facing the armature structure, a spring pressed plunger having a reduced end extending through and beyond the smaller diameter of the passage and an enlarged portion in the larger diameter of the passage, a spring in the stepped passage bearing against said enlarged portion, and an adjusting screw extending through the core from its other end into engagement with said spring for varying the force the spring exerts on the plunger, said spring pressed plunger being adapted to separate said armature structure and electromagnetic structure by pushing against said armature structure and reacting against said electromagnetic structure when the electromagnetic structure is deenergized.

References Cited UNITED STATES PATENTS 682,377 9/1901 Wurrnb 335-274 X 2,088,565 8/1937 Arrogg 335-274 2,441,041 5/1948 StaSzak 335274 X 2,871,676 2/1959 Miller 292-2515 X 2,877,041 3/1959 Foley 292251.5 3,204,154 8/1965 Crandell 292-25l,5 X

FOREIGN PATENTS 901,678 1/1954 Germany.

MARVIN A. CHAMPION, Primary Examiner E. I. MCCARTHY, Assistant Examiner U.S. Cl. X.R. 335-289 

